This invention concerns a process for starting, or start-up of, a high pressure gas discharge lamp for motor vehicles in which an alternating voltage is developed from a direct voltage, the alternating voltage is fed to an ignition device to ignite the high pressure gas discharge lamp, a lamp voltage and/or a lamp current is measured, an actual value of the lamp current and/or voltage is compared with a desired value and for a predetermined time span after ignition of the high pressure gas discharge lamp an additional power is added to an operating power of the high pressure gas discharge lamp by means of changing the alternating voltage which, on one hand, is limited by a maximum permissible lamp current and, on the other hand, is reduced after elapse of the predetermined time span. The invention also concerns an apparatus therefor as per the preamble of claims 10 and 14.
From German Offenlegungsschrift DE-OS 37 29 383, concerning a switching, or circuit, arrangement to start a high pressure gas discharge lamp, a process is known for starting a high pressure gas discharge lamp in which an alternating voltage is developed from a direct voltage and this alternating voltage is fed to an ignition device for igniting a high pressure gas discharge lamp. In a circuit of the lamp and in an alternating voltage producer, or converter, voltages are measured which are compared as actual values with desired values and, in dependence thereon, power fed to the lamp is changed. So that the lamp achieves, with high dependability, a stable operational condition after ignition, an additional power is added to operational power fed to the high pressure gas discharge lamp by means of changes in the alternating voltage for a predetermined time period dependent upon a measured actual voltage value. The changes in the alternating voltage result from increases of a monitored start condition during and directly after ignition of the high pressure gas discharge lamp as opposed to a sensed condition during normal operation.
It has shown itself to be disadvantageous for the high pressure gas discharge lamp, after ignition, to be fed a constant or uniform additional power during which the high pressure gas discharge lamp, in particular after only a short interruption of operation, upon being switched on gives off a high light strength which can lead to a blinding effect, which, in particular for motor vehicles, can lead to dangerous situations.
In addition, it has proven to be disadvantageous that the high pressure gas discharge lamp according to various existing start-up conditions commences operation with various light strengths and thereby does not achieve a possibly quicker, or a uniform, steady increase of light strength as quickly as possible.
The circuit arrangement comprises a direct voltage source which is connected to an alternating voltage producer, or converter, an ignition device between the alternating voltage converter and the high pressure gas discharge lamp, at least one voltage measuring device in a lamp circuit and a comparator which controls the alternating voltage producer in order to change the alternating voltage.
An object of this invention is to provide a process and an apparatus for starting high pressure gas discharge lamps in motor vehicles that are uncomplicated and cost effective and that assure that the high pressure gas discharge lamps reach their optimal operational conditions independently of start-up conditions as quickly as possible, without exceeding desired light outputs, thereby causing a blinding effects, with even, regular increases of light power outputs.